Manufacture of lithopone



May 15, 1928.

w. H. LANDERS MANUFACTURE oF LITHoPoNE Filed Feb. 2l, 1925 mwN Patented May 15, 1928.

UNITED STATES PATENT oFElcE.

mnracrunn or LITHoPoNn.

Application 'led February 21, 1925. Serial Io. 10,758..

invention relates to the manufacture f lithopone and hasfor'its principal object the provision of-an improved apparatusfor and method of drying and calcining-litho- I pone.

In the manufacture of lithopone, the precipitate of zinc sulfide and barium sulfate resulting from the interaction of solutions of Vzinc sulfate and barium sulfide is usu- RO ally lter-pressed, is dried in any suitable apparatus, and after the drying operation, is heated or calcined and the hot product plunged directly from the heating chamber into cold water. Heretofore emphasis has been placed on the necessity of drying the rawmaterial prior to calcination and very low percentages, say from 3% to 10% have been considered as the maximum limits for the residual moisture in the lithopone when Q0 ready for calcination; and the present invention eliminates this drying operation heretofore thought necessary prior to calcining. According to my invention, undried lithopone, either the wet precipitate or `^slurry as it comes from the precipitating tank, or the very moist cake resulting from a iiltering operation is introduced into a furnace without the drying operation .heretofore considered essential. The lithopone e0 gradually Works its Way toward the discharge end of the furnace, being first dried, then preheated, then calcined and finally discharged into cold water. lPreferably the furnace is heated internally by means of gas' that is supplied with an insufficient amount of air to 'completely consume the gas in the calcining zone of the furnace.

A further development of the invention relates to the burning of the unconsumed 40 fuel gas at such points in the furnace or Inutile as are maintained at a temperature lower than that at which the Zinc sulfide will be oxidiaed, the necessary air being admitted in carefully controlled quantities through,

the Walls of the furnace. Thecxtra heat thus generated is used to more quickly and economically dry or preheat the material before it is advanced to the zone of higher or calcining temperatures. The extra. heat gained in this manner is secured at little or no additional cost, because, as has been stated, it is necessary to have the gas in the calcining portion of the furnace in excess of the air suliicient to completely burn it, and this excess gas is ordinarily wasted and by using said excess gas, the capacity' `ofthe furnace is greatly increased.

The accompanying drawing which forms part of this specification, is a longitudinal sectional view of a furnace embodying my invention. In carrying out myinvention, I prefer to use a revolving cylinder 1 slightly inclined from the receiving toward the discharge end and of sufficient length and diameter to give the capacity desired. The furnace l is-pro vided with rings 2 that rest on anti-friction rollers 3 and suitable means for rotatin it are provided, as a ring gear 4 on the rnace that mesheswith a gear 5 driven IYin any suitable manner. Preferably thrust rollers 6 are mounted on either side of the rings 2.

The cylinder 1 is lined with brick 7 or other insulating or refractory-material in such portions as are subjected to high temperature or as are necessary to protect the crude or raw lithopone from contact with the metallic walls of the cylinder--and'consequent discoloration of the lithopone. At the feed end is illustrated a pump 8 for feeding lithopone in the form of a slurry 9 into the furnace. Any other suitable device for y'feeding slurry or moist filter cake into the furnacel may be used.

The kiln or furnace thus described is providedwith a closure plate 10 and a closure 4*ring 11 constituting -an air seal at the discharge or firing end to prevent vthe entrance of -air other than that mixed with the fuel. A gas burner 12 preferably of the Bunsen type, extends into the furnace aty the discharge end; and as has been stated, the burner is supplied with air in insuiiicient quantities to completely burn the gas. Thus the gas burns with a reducing flame in the calcining portion of the furnace and there ings are equipped with valves 16 or other air controlling devices tol permit careful control ofthe amount of air to be admitted. A considerable amount of unconsumed fuel gas reaches the immediate vicinity of one or more of the auxiliary air vvents 15 described above because of the insutiicientf air supply at the burner 12. This unconsumed gas unites with the oxygen entering'through the air vents 15 and assists in drying the raw lithopone. The temperature thus created is not high-enough, to oxidize any part of the raw lithopone. The exhaust tgases pass out through a `stack 17 at the feed end of the furnace. l

Into the feed or cold end of' this furnace is fed the crude lithopone from the precipitating vats, either without previous dewatering or after filtering, without other drying in the form of a slurry or Wet filter cake. This can be introduced by a pump, as illustrated, or by a jet, screw conveyor or other means, avoiding the necessity of providing separate drying apparatus with its attendant cost and possible injury to the crude lithopone. The crude lithopone is caused bythe design of the furnace to travel towards the calcining or high temperature zone, and is successively dried, preheated, calcined and finally discharged at a red heat into the quench box. At all stages of this operation the amount of heat, proportion of air and reactivity of the fuel gas are under control resulting in a calcined lithopone of superior color and opacity, and greatly reducing the cost of making lithopone without impairing its desirable qualities. If the temperature of the furnace outside of the calcining zone becomes too high, the amountof air introduced through the auxiliary vents can be increased, 'thus cooling the furnace.

It will be understood that the furnace may be made and used Without the auxiliary air inletpipes hereinbefore described. As

has been sta-ted, if air inlets are used, carel must be taken that, in the calcining zone,

t there is insufficient air to completely consume the fuel.

Obviously numerous changes may be made without departing from the invention and I do not `Wish to be limited to the precise embodiments of the invention hereinbefore set forth. i

What I claim is:

1. The improvement in the process of making lithopone, which comprises carrying on the entire drying and calcining thereof as one continuous operation in. one vessel by burning fuel inside of said vessel in the same chamber with the lithopone said fuel being supplied with an insufficient amount of air to completely consume the combustible matter thereof in the calcining zone.

2. The improvement in the process of making lithopone, which comprises carrying on the entire drying and calcining thereof as one continuous operation in one vessel by burning fuel inside of said vessel in the same chamber with the lithopone, and regulating the temperatureV of the furnace outside of the calcining zone by the admission of air into the furnace.

3. The process of .treating undried raw lithopone which consists in passing such lithopone through an elongated combustion chamber in one direction, burning fuel in the lithopone discharge end portion of said chamber, and passing the products of oombustion through said chamber in the opposite direction, the' fuel for such combustion being fed into said lithopone discharge end portion with insuiiicient air to effect complete combustion in such end portion whereby the raw lithopone is dried and calcined.

4. The process of treating undried raw lithopone which consists in passing suchv lithopone through an elongated combustion chamber in one direction, burning fuel in the lithopone discharge end portion of said chamber, and passing the products of combustion through said chamber in the opposite direction, the fuel lfor such combustion being fed into said lithopone discharge end portion with insuiiicient air to effect complete combustion in such end portion whereby the raw lithopone is dried and calcined, and additional air being fed into said chamber back from said discharge end for burning the combustible matter in said products of the main combustion.

5. The improvement 'in the process of making lithopone, which comprises feeding undried lithopone into one end of an elongated slightly inclined furnace, rotating said furnace to cause the lithopone to move toward the other end f the furnace, introducing combustible gas into said furnace at the end opposite that at which the lithopone is introduced and burning said gas in the presence of air in insutiicient quantity to complctelv consume the gas.

. 6. The improvementV in the process of makin lithopone, which comprises feeding undried lithopone into one end of an elongated slightly inclined furnace, rotating said furnace to cause the lithopone to move toward the other end of the furnace, introducing combustible gas into said furnace at the end opposite that at which the lithopone is introduced. burning said gas in the presence'of air in insufficient quantity to completely consume the gas, whereby the litho- -pone is first dried. then preheated and finally calcined. andiintroducing air into the furnace between the calcmlng portion and the fccd end thereof.

7. The process of making lithopone which comprises feeding into the upper end of an elongated inclined furnace. lithopone con taining 1n excess of 10% moisture, `heating www@ 31,

the lower @md said furnace by burning the upper end of Mh@ umacj ibo the iowa@ fuel iherein in the presence of am insucent end thereof, im be @rst dried 'and than wl amount of air to compltey consume @he cined.

neL thareby cacining the lithopone in the Sigmd at (Collinsville9 lUil'noisj this 22nd lower and ih@ furnace and drying the day of Jaznumy, 1925.

moist ithopone in the upper end the :'Em-

mace, the ithopone passing gradualy wm WILLIAM ERS., 

